Carbohydrate malabsorption and the effect of dietary restriction on symptoms of irritable bowel syndrome and functional bowel complaints.

BACKGROUND: Carbohydrate malabsorption of lactose, fructose and sorbitol has already been described in normal volunteers and in patients with functional bowel complaints including irritable bowel syndrome. Elimination of the offending sugar(s) should result in clinical improvement.

OBJECTIVE: To examine the importance of carbohydrate malabsorption in outpatients previously diagnosed as having functional bowel disorders, and to estimate the degree of clinical improvement following dietary restriction of the malabsorbed sugar(s).

METHODS: A cohort of 239 patients defined as functional bowel complaints was divided into a group of 94 patients who met the Rome criteria for irritable bowel syndrome and a second group of 145 patients who did not fulfill these criteria and were defined as functional complaints. Lactose (18 g), fructose (25 g) and a mixture of fructose (25 g) plus sorbitol (5 g) solutions were administered at weekly intervals. End-expiratory hydrogen and methane breath samples were collected at 30 minute intervals for 4 hours. Incomplete absorption was defined as an increment in breath hydrogen of at least 20 ppm, or its equivalent in methane of at least 5 ppm. All patients received a diet without the offending sugar(s) for one month.

RESULTS: Only 7% of patients with IBS and 8% of patients with FC absorbed all three sugars normally. The frequency of isolated lactose malabsorption was 16% and 12% respectively. The association of lactose and fructose-sorbitol malabsorption occurred in 61% of both patient groups. The frequency of sugar malabsorption among patients in both groups was 78% for lactose malabsorption (IBS 82%, FC 75%), 44% for fructose malabsorption and 73% for fructose-sorbitol malabsorption (IBS 70%, FC 75%). A marked improvement occurred in 56% of IBS and 60% of FC patients following dietary restriction. The number of symptoms decreased significantly in both groups (P < 0.01) and correlated with the improvement index (IBS P < 0.05, FC P < 0.025).

CONCLUSIONS: Combined sugar malabsorption patterns are common in functional bowel disorders and may contribute to symptomatology in most patients. Dietary restriction of the offending sugar(s) should be implemented before the institution of drug therapy.